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Did a bit of Moon observing ...


vlaiv

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It's been a month now, I think, since I was last time under stars, and I can't remember when was the last time I was observing. Most of my time under stars is currently dedicated to imaging.

So last couple of weeks were filled with clouds, a bit of flu / cold, business travel, ... and I was craving astro fix, big time :D. Weather forecast was promising, and since I'm not fully on my feet to hit the yard and pull out big guns, I decided to do a sort of grab'n'go on my south facing balcony. It was still daytime when I noticed that moon was looking really good. It is one of those observing targets that I always wanted to visit in more detail but never got around to actually do it. Sneak peek to satisfy my astro craving was in order! Weapon of choice: SW ST 102 F/5 achro :D. I know, I know, not the best scope for the task, but I wondered how much would I get out of it. There is old saying: Moon looks good in any decent scope.

Eyepieces used: ES82 11mm - I've got this eyepiece some time a go but still have not used it in anger, 7mm TMB clone, APM x2.7 barlow to pump up the mag. Scope was mounted on AZ-4 with steel tripod (very solid and nice in use).

ES82 11mm is a bit acquired taste for me, still not quite used to ergonomics of it, field is just huge, and although eye lens is a bit recessed, having long eyelashes, going in for full FOV just feels a bit uncomfortable for me. But I decided that I need more practice with it :D, that and longer FL of the two I brought out, meant it was first in diagonal. First look - smack in the face! CA was just all over the place, completely intolerable!

Aperture mask to the rescue! ST102 comes with front cover that has 50mm hole in it - one just needs to remove cap. This makes it 50mm F/10 scope. I quickly popped on front cover with smaller hole cap removed - CA vanished instantly! View got quite a bit darker but also a lot sharper. This was at ~ x45.5, so well under max mag for "50mm" scope. Seeing was average, more shimmer type than blurring - mostly due to local thermals rather than high altitude disturbances. I started by just looking at the full disk rather than any particular feature - I was amazed to see complete orb, even half that was in shadow, due to earth shine. Numerous times previously when I was looking at the moon by naked eye, it looked like full moon disk can be seen, but I always wondered if my eyes and brain are playing a trick on me, and I was imagining seeing it because it ought to be there, rather than actually seeing it.

Next I started playing around with magnification and comparing eyepieces. Putting barlow in resulted in larger image but it was immediately clear that it was too much magnification for 50mm mask. There was soft feel to smallest features, and it was obvious that more detail is there than being rendered. So I decided to remove aperture mask and just put up with CA. For some reason ES82 11mm with APM x2.7 was "more sensitive" to CA - it bothered me more than when I used 7mm TMB. I also noticed that I have too much mag to cope with such CA levels - things were a bit sharper than with 50mm mask but still blurry and soft.

By this time I concentrated my observing to Theophilus, Cyrillus and Catherina region. Not that I knew at that time names of those craters - I'm just reading them from Moon atlas as I'm writing this :D. It was just interesting region and there were a lot of small craters south of Cyrillus F which I used to judge sharpness of view. 

Next I remembered that there is something I can use to enhance view quite a bit. I don't own any CA removing filter, but I do have quite a bit of narrow band filters, so I opted for one that is well suited for visual and not very narrow to avoid too much light being blocked. Baader Solar Continuum filter - it is centered around 540nm, so green image, and I judge FWHM to be around 10nm. So I screwed it on the eyepiece and behold - sharpness of the razor comes to mind! Apart of image being really green, which bothered me a bit until I got used to it, and quite a bit darker, but not too dark, especially after a bit when eyes adjust, this filter is superb for observing with fast achromat. Image is so sharp, and even seeing influence is reduced. Features and small craters just became visible. This is the spot where I hit next blurring obstacle - this time eyepiece. TMB 7mm is just not sharp enough to qualify as top tier planetary / lunar eyepiece (maybe 3.5 out of 5 "stars" :D ). I felt there was more to be seen with the scope in this configuration and seeing but eyepiece would not let me. ES82 11mm on the other hand was sharper and better, but similar level of detail was seen just because it could not reach necessary magnification to show all it could show - I was limited to ~x122 with this eyepiece.

Other features that I've payed attention to include (bear with me on this, I'm still using Moon atlas and learning feature names :D ) - Torricelli 1 (a plateau like feature between Torricelli crater and Theophilus), Beaumont C, G and J and some smaller unnamed craters around those and I finished with Aristoteles - which was a beautiful sight - light was at such angle that only rim of crater was visible - interior of crater was completely in shadow - it just looked like big hole, no way of judging it's depth.

So that was it for tonight, at least in regards to Moon gazing, scope is still out, and I might go one more round looking for Uranus and Neptune later on if weather continues to cooperate (forecast predicts clouds again around midnight).

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Great report vlaiv! I enjoyed reading that one, you certainly had some fun challenging your achromatic to do things it's not supposed to be good at :) 

I was looking at the moon earlier too, and enjoyed some similar targets, as well as the lovely earthshine you describe.

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Nice report thanks for posting. I try the same things on the moon with my st120 and also have a great time with it even though it's not designed with that in mind. It's good fun and good for learning things for yourself  to have a go at any target in any scope.

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22 hours ago, Paz said:

Nice report thanks for posting. I try the same things on the moon with my st120 and also have a great time with it even though it's not designed with that in mind. It's good fun and good for learning things for yourself  to have a go at any target in any scope.

So true!  I find the Moon does well in the ST120 - especially now that I've bought a WO SPL 3mm, which gives a healthy x200!  (Never been fond of Barlows,  i.e. adding adding extra bits!)

Doug.

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